Underground gasification ignition method

ABSTRACT

An underground gasification ignition method comprises the following steps: making a directional drilling and a vertical well to construct an underground gasification furnace; using a cold fracturing method to pre-penetrate a coal seam; and igniting in the vertical well at an end of the directional drilling.

TECHNICAL FIELD

The present invention relates to a method of underground gasification ignition, applicable in fields such as underground coal gasification.

BACKGROUND

The underground coal gasification is a process in which the underground coal is transferred in situ into combustible gas through thermal chemistry reaction. As a clean coal technology, underground coal gasification has obvious technological advantages in mining low grade coal seam, deep coal seam, thin coal seam and three under-coals (under waters, buildings or roads), thus being particularly suitable for the energy resource situation of amplitude of coal, short of oil and deficiency of gas. The technology of underground coal gasification has the economical and social benefits of small investment, short construction period and friendly circumstance, thus it has received highly attention in the international coal industry. In recent few years, as the energy situation becomes more and more stressful, science research colleges and institutes and related enterprises have made much effort on development of underground coal gasification technology, thus it has a fast development.

In the application of underground coal gasification technology, ignition in the gasification furnace and penetration and processing of a channel are very important procedures. In the current underground gasification process, channel processing often employs air firepower percolation method, hydraulic fracturing method and electrical penetration method, of which the penetration speeds are comparatively slow.

The existing underground gasification ignition method mainly followed a certain order. Firstly, a vertical well should be created, and then light a fire in the vertical well. After the fire zone was established in the vertical well bottom, the directional drillings were created. Because of the established fire zone, the directional drillings were actually processed in hot state. And after that, the channel was penetrated through the fire. Since that only vertical wells were processed when igniting, so the penetration speeds between the vertical wells were slow, and more time should be used to penetrate the wells. It means that flame moving slowly would result in low efficiency.

SUMMARY OF THE INVENTION

Against the shortcomings of the prior art, the present invention aims to provide a method of underground coal gasification ignition, in particular relates to a method of underground gasification ignition comprising the following steps:

-   (1) creating a directional drilling and vertical well(s) to     construct an underground gasification furnace; -   (2) pre-penetrating the coal seam in the method of cold fracturing; -   (3) igniting in the vertical well at the end of the directional     drilling. In the present invention, firstly the directional drilling     and vertical well are created to construct an underground     gasification furnace. Then the coal seam in the gasification furnace     is fractured in cold the status and ignition is made in the vertical     well at the end of the directional drilling. This method has the     advantages of high ignition efficiency and fast penetrating speed.

The following is described as the preferred technical solutions of the present invention, but not as the restriction for the technical solutions provided by the present invention. With the following technical solutions, the technical goal and beneficial effect of the present invention can be achieved in a better way.

Optionally, on the basis of the technical solutions provided by the present invention, step (4) is conducted after the step (3), wherein after ignition source is formed, gas inlet hole and gas outlet hole are switched and the gasification channel is processed with firepower.

Optionally, on the basis of the technical solutions provided by the present invention, in the step (4) gas inlet hole and gas outlet hole are switched to the status that gas is discharged through the ignition vertical well.

Optionally, on the basis of the technical solutions provided by the present invention, in the step (4) the ignition source is considered to be formed when the coal-burning volume is ≧0.5 cubic meters.

Preferably, on the basis of the technical solutions provided by the present invention, the number of the vertical well is 1.

In the step (3), ignition is made in the vertical well at the end of the directional drilling and gas is discharged through the directional drilling. Preferably, on the basis of the technical solutions provided by the present invention, the number of the vertical wells is at least 2.

In the step (3), ignition is made in one of the vertical wells at the end of the directional drilling, and gas is discharged through at least one of the other vertical wells and pressure maintenance is made for the directional drilling at the same time. Preferably, on the basis of the technical solutions provided by the present invention, the pressure maintenance in step (3) is maintaining pressure within 0.3-1.0 MPa.

Preferably, on the basis of the technical solutions provided by the present invention, the coal is brown coal and the vertical distance between the vertical well and the directional drilling channel is 2-10 meters.

Preferably, on the basis of the technical solutions provided by the present invention, the coal is bituminous coal and the vertical distance from the vertical well to the directional drilling channel is 1-5 meters.

Preferably, on the basis of the technical solutions provided by the present invention, the gasification agent used for ignition is oxygen-containing gas and its oxygen concentration is ≧21%.

Compared with the prior art, the present invention has the following beneficial effect: in the present invention, directional drilling and vertical well are firstly created to construct an underground gasification furnace; the coal seam is pre-penetrated in the manner of cold fracturing; ignition is made in the vertical well at the end of the directional drilling. The method of the present invention has advantages of high ignition efficiency and fast penetrating speed.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows the process flow chart of the ignition method of Example 1.

FIG. 2 shows the side view of the ignition process of Example 1.

FIG. 3 shows the vertical view of the ignition and penetration process of Example 1.

FIG. 4 shows the side view of the ignition process of Example 2.

FIG. 5 shows the vertical view of the ignition and penetration process of Example 2.

FIG. 6 shows the process flow chart of the ignition method of Example 3.

FIG. 7 shows the side view of the ignition process of Example 3.

FIG. 8 shows the vertical view of the ignition and penetration process of Example 3.

FIG. 9 shows the process flow chart of the ignition method of Example 4.

FIG. 10 shows the side view of the ignition process of Example 4.

FIG. 11 shows the vertical view of the ignition and penetration process of Example 4.

DETAILED DESCRIPTION

For better illustrating the present invention and understanding of the technical solutions of the present invention, the typical but non-limiting embodiments of the present invention are described in the following:

In a typical embodiment of the present invention, an underground gasification ignition method comprises the following steps:

-   (1) creating a directional drilling and vertical well(s) to     construct an underground gasification furnace; -   (2) pre-penetrating the coal seam in the manner of cold fracturing; -   (3) igniting in the vertical well at the end of the directional     drilling. In the present invention, firstly directional drilling and     vertical well are created to construct the underground gasification     furnace; the coal seam is pre-penetrated in the manner of cold     fracturing; ignition is made in the vertical well at the end of the     directional drilling. In the present invention, firstly a     gasification furnace composed of directional drilling and vertical     well is constructed and ignition in vertical well is made after cold     fracturing. When first creating directional drilling then conducting     the fracturing, the fracturing efficiency is improved because a     horizontal channel has been formed and penetration is speeded up     after the ignition of the fractured channel; the ignition efficiency     is improved because the fire work face movement is faster; and it is     beneficial to the future operation of the gasification furnaces     composed of directional drillings, because the current industrial     gasification furnaces are usually composed of directional drillings.

Moreover, the present invention also overcomes the disadvantage of the prior art than burning area is firstly constructed in the bottom of the vertical well and then the directional drilling is processed at high temperature, thus the holing through process is greatly affected by the processing of directional drilling.

According to the present invention, the step (4) is conducted after the step (3), wherein after the ignition source is formed, gas inlet hole and gas outlet hole are switched and the gasification channel is processed with firepower. According to the present invention, in the step (4), the gas inlet hole and gas outlet hole are switched to the status that gas is discharged through the vertical well.

According to the present invention, in the step (4), the ignition source is considered to be formed when the coal-burning volume is cubic meter.

The step (4) of the present invention further comprises a reliable control method on the basis of previous steps, wherein whether ignition source has been formed is determined by coal-burning volume at the coal gas outlet hole, thus gas inlet hole can be switched in time, preventing from the collapse of top plate of the coal seam induced by partial channel being too wide.

According to the present invention, when the number of the vertical well is 1, in the step (3) ignition is made in the vertical well and gas is discharged through directional drilling. When the coal-burning volume is ≧0.5 cubic meter, ignition source is considered to be formed, then the gas outlet hole and gas inlet hole are switched to the status that gas is introduced through the directional drilling and discharged through the vertical well.

According to the present invention, when the number of the vertical wells is at least 2, in the step (3) ignition is made in one of the vertical wells at the end of the directional drilling, gas is discharged in at least one of the other vertical wells and pressure maintenance is made for the directional drilling at the same time.

When the number of the vertical wells is 2, in the step (3) ignition is made in one of the vertical wells and gas is discharged in the other vertical well. When the coal-burning volume is ≧0.5 cubic meter, the ignition source is considered to be formed. Then the gas outlet hole and gas inlet hole are switched according to the position of the ignition hole to the status that gas is introduced through directional drilling or the previous gas outlet vertical well, and gas is discharged through the ignition vertical well, all of which aim to process the gasification channel with firepower so as to penetrate the gasification channel.

When the number of the vertical wells is at least 3, in the step (3) firstly any one of the vertical wells is selected for ignition, and gas is discharged through at least one of the other vertical wells. When the coal-burning volume is ≧0.5 cubic meter, the ignition source is considered to be formed, then the gas outlet hole and gas inlet hole are switched according to the position of the ignition hole to the status that gas is introduced through the directional drilling, an auxiliary well or the previous gas outlet well, and gas is discharged through the ignition vertical well, all of which aim to process gasification channel with firepower so as to penetrate the gasification channel. The auxiliary wells are the vertical wells other than the ignition vertical well and the previous gas outlet well in the step (3).

In the step (3) of the present invention, pressure maintenance is made for directional drilling in the process of vertical well ignition and penetration, in order to prevent from the occlusion induced by late use after the directional drilling is finished and also to effectively prevent from the entry of underground water.

The number of the vertical wells is at least one, such as 1, 2, 3, 4, 5, 6, 7, etc.

The aperture diameter of the vertical well is 200-400 mm, such as 220 mm, 240 mm, 260 mm, 280 mm, 300 mm, 320 mm, 340 mm, 360 mm or 380 mm.

The distance from the bottom of casing tube of the vertical well to the bottom plate of the coal seam is 1-2 meters.

The channel of the directional drilling is an unsupported channel or a supported channel with sieve-tube.

The length of the directional drilling channel is 70-150 meters, such as 80 meters, 90 meters, 100 meters, 110 meters, 120 meters, 130 meters, or 140 meters.

The aperture diameter of the directional drilling is 100-250 mm, such as 110 mm, 120 mm, 140 mm, 160 mm, 180 mm, 200 mm, 220 mm, 240 mm or 245 mm.

In the present invention, the vertical well is not directly connected with the directional drilling. When the coal is brown coal, the vertical distance between the vertical well and the directional drilling channel is 2-10 meters, such as 3 meters, 4 meters, 5 meters, 6 meters, 7 meters, 8 meters or 9 meters. When the coal is bituminous coal, the vertical distance between the vertical well and the directional drilling channel is 1-5 meters, such as 1.5 meters, 2 meters, 2.5 meters, 3 meters, 3.5 meters, 4 meters or 4.5 meters.

The fracturing method is any one of the methods of hydraulic fracturing, high-pressure air permeation, blasting or chemical solution breaking.

The ignition in the vertical well is any one of electric ignition, solid fuel ignition or coke ignition.

The gasification agent used for ignition is oxygen-containing gas and its oxygen concentration is 21%, such as 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

The pressure maintenance of the step (3) aims to keep pressure within 0.3-1.0 Mpa, such as 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 Mpa or 0.9 Mpa. The pressure maintenance can be realized by continuously aerating the directional drilling.

The beneficial effects of the present invention will be further illustrated in the following referring to the specific embodiments and specific examples.

Embodiment 1

A method of underground gasification ignition comprising the following steps:

-   (1′) creating a directional drilling and a vertical well to     construct an underground gasification furnace, wherein the number of     the vertical well is 1; -   (2′) pre-penetrating coal seam in the manner of cold fracturing; -   (3′) igniting in the vertical well at the end of the directional     drilling. -   (4′) when the coal-burning volume is ≧0.5 cube meter, a ignition     source being considered to be formed; then it being switched to the     status that gas is introduced through the directional drilling, and     gas is discharged through the vertical well and the gasification     channel being processed with firepower.

Embodiment 2

A method of underground gasification ignition comprising the following steps:

-   (1′) creating a directional drilling well and vertical wells to     construct an underground gasification furnace, wherein the number of     the vertical wells is 2; -   (2′) pre-penetrating coal seam in the manner of cold fracturing; -   (3′) igniting in one of the vertical wells at the end of the     directional drilling; gas being discharged through the other     vertical well; pressure maintenance being made for the directional     drilling during the process of the vertical well ignition and     penetration; -   (4′) when the coal-burning volume is ≧0.5 cubic meter, a ignition     source being considered to be formed; then it being switched     according to the position of ignition hole to the status that air is     introduced through the directional drilling, and gas is discharged     through the ignition vertical well and the gasification channel     being processed with firepower.

Embodiment 3

A method of underground gasification ignition comprising the following steps:

-   (1′) creating a directional drilling and vertical wells to construct     an underground gasification furnace, wherein the number of the     vertical wells is 2; -   (2′) pre-penetrating coal seam in the manner of cold fracturing; -   (3′) igniting in one of the vertical wells at the end of the     directional drilling; gas being discharged through the other     vertical well; pressure maintenance being made for the directional     drilling during the process of vertical well ignition and     penetration; -   (4′) when the coal-burning volume is ≧0.5 cube meter, a ignition     source is considered to be formed; then it being switched according     to the position of ignition hole to the status that gas is     introduced through the previously gas outlet vertical well, and gas     is discharged through the ignition vertical well, and the     gasification channel being processed with firepower.

Embodiment 5

A method of underground gasification ignition comprising the following steps:

-   (1′) creating a directional drilling and vertical wells to construct     an underground gasification furnace, wherein the number of vertical     wells is at least 3; -   (2′) pre-penetrating coal seam in the manner of cold fracturing; -   (3′) igniting in one of the vertical wells at the end of the     directional drilling; gas being discharged through at least one of     the other vertical wells; pressure maintenance being made for the     directional drilling during the process of vertical well ignition     and penetration; -   (4′) when the coal-burning volume is ≧0.5 cube meter, a ignition     source is considered to be formed; then it being switched according     to the position of ignition hole to the status that gas is     introduced through the directional drilling, and gas is discharged     through the ignition vertical well, and the gasification channel     being processed with firepower.

Embodiment 6

A method of underground gasification ignition comprising the following steps:

-   (1′) creating a directional drilling and vertical wells to construct     an underground gasification furnace, wherein the number of the     vertical wells is at least 3; -   (2′) pre-penetrating the coal seam in the manner of cold fracturing; -   (3′) igniting in one of the vertical wells at the end of the     directional drilling; gas being discharged through at least one of     the other vertical wells; pressure maintenance being made for the     directional drilling during the process of vertical well ignition     and penetration; -   (4′) when the coal-burning volume is ≧0.5 cubic meter, a ignition     source is considered to be formed; then it being switched according     to the position of ignition hole to the status that air is     introduced through the previous gas outlet vertical well, and gas is     discharged through the ignition vertical well, and the gasification     channel being processed with firepower.

Embodiment 7

A method of underground gasification ignition comprising the following steps:

-   (1′) creating a directional drilling and vertical wells to construct     an underground gasification furnace, wherein the number of the     vertical wells is at least 3; -   (2′) pre-penetrating coal seam in the manner of cold fracturing; -   (3′) igniting in one of the vertical wells at the end of the     directional drilling; gas being discharged through at least one of     the other vertical wells; pressure maintenance being made for the     directional drilling during the process of the vertical well     ignition and penetration; -   (4′) when the coal-burning volume is ≧0.5 cubic meter, a ignition     source is considered to be formed; then it being switched according     to the position of ignition hole to the status that gas is     introduced through the auxiliary well, and gas is discharged through     the ignition vertical well, and the gasification channel being     processed with firepower.

Example 1

Example 1 relates to a process, wherein one directional well and one vertical well are coordinately used for ignition in the brown coal seam. This process has the advantages of high fracturing efficiency, good dewatering effect of gasification furnace and high ignition efficiency, thereby providing superior precondition for industrial application of underground gasification furnace.

Referring to FIGS. 1-3, the present example mainly comprises the following steps:

-   (1) an underground gasification furnace composed of one directional     well and one vertical well along a line near an end of the     directional drilling is constructed in the brown coal seam, wherein     the coal seam is of 10 meters thick, the aperture diameter of the     directional drilling is 150 mm, the channel is unsupported channel,     the horizontal distance is 150 m, the aperture diameter of the     vertical well is 250 mm, which is located at the side of the     directional drilling line, and the bottom of the casing tube is of     about 2 m away from the bottom plate of the coal seam and of 10 m     away from the directional drilling channel vertically; -   (2) high pressure air permeation method is used to conduct cold     fracturing for the underground gasification furnace and the channel     between the directional drilling and vertical well is penetrated. -   (3) solid fuel is put down in the vertical well as the ignition     well; air is used as gasification agent; gas is discharged through     the directional drilling; ignition source is cultivated, wherein     whether the ignition source is formed is determined by coal-burning     amount at coal gas outlet hole; -   (4) when the coal-burning volume is 0.5 cubic meter, the ignition     source is considered to be formed; gas outlet hole and gas inlet     hole are switched to the status that air is introduced through the     directional drilling, and gas is discharged through the vertical     well; reverse ignition is made to penetrate the gasification     channel.

Example 2

Example 2 relates to a process, wherein one directional well and one vertical well are coordinately used for ignition in the bituminous coal seam. This process has the advantages of high fracturing efficiency, good dewatering effect of gasification furnace and high ignition efficiency, thereby providing superior precondition for industrial application of underground gasification furnace.

Referring to FIGS. 4-5, the present example mainly comprises the following steps:

-   (1) an underground gasification furnace composed of one directional     well and one vertical well along a line near an end of the     directional drilling is built up in the bituminous coal seam,     wherein the coal seam is of 10 meters thick, the aperture diameter     of the directional drilling is 150 mm, the channel is unsupported     channel, the horizontal distance is 120 m, the aperture diameter of     the vertical well is 300 mm, which is located at the side of the     directional drilling line, and the bottom of the casing tube is     about 2 m away from the bottom plate of the coal seam and of 5 m     away from the directional drilling channel vertically; -   (2) chemical solution breaking method is used to conduct cold     fracturing for the underground gasification furnace and the channel     between the directional drilling and vertical well is penetrated; -   (3) coke is put down in the vertical well as the ignition well; air     containing 35% oxygen is used as gasification agent; gas is     discharged through the directional drilling; ignition source is     cultivated, wherein whether the ignition source is formed is     determined by the coal-burning amount at the coal gas outlet hole; -   (4) when the coal-burning volume is ≧0.5 cubic meter, the ignition     source is considered to be formed; gas outlet hole and air inlet     hole are switched to the status that air is introduced through the     directional drilling, and gas is discharged through the vertical     well; reverse ignition is made to penetrated the gasification     channel.

Example 3

Example 3 relates to a process, wherein one directional well and three vertical wells are coordinately used for ignition in the brown coal seam. This process has the advantages of high fracturing efficiency, good dewatering effect of gasification furnace and high ignition efficiency, thereby providing superior precondition for the sequential operation of gasification furnace composed of directional drilling.

Referring to FIGS. 6-8, the present example mainly comprises the following steps:

-   (1) an underground gasification furnace composed of one directional     well and 1#, 2# and 3# vertical wells along a line near an end of     the directional drilling is constructed in the brown coal seam,     wherein the coal seam is of 10 meters thick, the aperture diameter     of the directional drilling is 150 mm, the channel is unsupported     channel, the horizontal distance is 150 m, the vertical wells is     located at the two sides of the directional drilling line, the     bottom of casing tube is about 2 m away from the bottom plate of the     coal seam, 1#, 2# and 3# wells have aperture diameters of 350 mm,     350 mm and 200 mm, respectively, and are 8 m, 10 m and 10 m,     respectively, away from the directional drilling channel vertically     and the 1# well is 30 m and 10 m, respectively, away from the 2# and     3# wells horizontally; -   (2) high pressure air permeation method is used to conduct cold     fracturing for the underground gasification furnace and the channel     between the directional drilling and vertical well is penetrated; -   (3) air is used as gasification agent and is continuously introduced     in the directional drilling for pressure maintenance; ignition is     made in 1# vertical well; gas is discharged through 2# vertical     well; ignition source is cultivated, wherein the ignition source is     considered to be formed when the coal-burning volume at the coal gas     outlet hole reaches 1 cubic meter; -   (4) after the ignition source is formed, air introduction in 1#     ignition well is stopped and it is switched to the status that air     is introduced in 3# vertical well and gas is discharged through 1#     vertical well.

Example 4

Example 4 relates to a process, wherein one directional well and 2 vertical wells are coordinately used for ignition in the bituminous coal seam. This process has the advantages of high fracturing efficiency, good dewatering effect of underground gasification furnace, high ignition efficiency, and rapid holing through for the vertical well, thereby being beneficial to the sequential operation of gasification furnace composed of directional drilling.

Referring to FIGS. 9-11, the present example mainly comprises of the following steps:

-   (1) an underground gasification furnace composed of one directional     well and 1# and 2# vertical wells along a line near an end of the     directional drilling is constructed in the bituminous coal seam,     wherein the coal seam is of 10 meters thick, the aperture diameter     of the directional drilling is 150 mm, the channel is disposed with     sieve-tube support, the horizontal distance is 120 m, the vertical     wells is located at the two sides of the directional drilling line,     the bottom of casing tube is about 2 m away from the bottom plate of     the coal seam, both 1# and 2#wells have aperture diameters of 250 mm     and are 5 m away from the directional drilling channel vertically,     and the distance between the two wells is 25 meters; -   (2) cold fracturing is made for the underground gasification furnace     and the channel between the directional drilling and vertical well     is penetrated; -   (3) air containing 30% oxygen is used as gasification agent and is     continuously introduced into the directional drilling for pressure     maintenance; coke ignition is made in 2# vertical well; gas is     discharged through 1# vertical well; ignition source is cultivated,     wherein whether the ignition source is formed is determined by the     coal-burning volume at the coal gas outlet hole; -   (4) when the coal-burning volume is ≧0.5 cubic meter, the ignition     source is considered to be formed; after the ignition source is     formed, air introduction in 2# ignition well is stopped and air is     introduced in the directional drilling instead; reverse ignition is     made; air is continuously introduced in the directional drilling;     gas outlet well is switched to 2# well to prolong the gasification     channel.

The applicant states that the present invention employs the above embodiments to describe the detailed methods of the present invention, but the present invention is not limited to the detailed above methods, i.e. it does not mean that the present invention must rely on the above detailed method to be implemented. Persons skilled in the art should understand any improvement of the present invention, the equivalent replacement to the raw materials of the present invention product, the addition of auxiliary ingredients and the selection of specific mode all fall into the protection scope and disclosure scope of the present invention. 

1. A method of underground gasification ignition, comprising the following steps: (1) creating a directional drilling and vertical well(s) to construct an underground gasification furnace; (2) pre-penetrating the coal seam in the manner of cold fracturing; and (3) igniting in the vertical well at the end of the directional drilling.
 2. The method according to claim 1, further comprising step (4) following step (3), wherein after an ignition source is formed, a gas inlet hole and a gas outlet hole are switched and a gasification channel is processed with firepower.
 3. The method according to claim 2, wherein the gas inlet hole and the gas outlet hole are switched to the status that gas is discharged through the ignition vertical well.
 4. The method according to claim 2, wherein the ignition source is considered to be formed when coal-burning volume is ≧0.5 cubic meter.
 5. The method according to claim 1, wherein the number of the vertical well is 1; and wherein in step (3) ignition is made in the vertical well at the end of the directional drilling and gas is discharged through the directional drilling.
 6. The method according to claim 1, wherein the number of the vertical wells is at least 2; and wherein in step (3), ignition is made in one of the vertical wells at the end of the directional drilling, gas is discharged through at least one of the other vertical wells and pressure maintenance is made in the directional drilling at the same time.
 7. The method according to claim 6, wherein the pressure maintenance is maintaining pressure within 0.3-1.0 MPa.
 8. The method according to claim 1, wherein the coal is brown coal and the vertical distance between the vertical well and the directional drilling channel is 2-10 meters.
 9. The method according to claim 1, wherein the coal is bituminous coal and the vertical distance between the vertical well and the directional drilling channel is 1-5 meters.
 10. The method according to claim 1, wherein oxygen-containing gas is used as a gasification agent for ignition and its oxygen concentration is ≧21%. 